1. Field of the Invention
The present invention relates to a lightning protection fastener used for an airframe of an aircraft, and especially for wings, as well as to a method for mounting the lightning protection fastener.
2. Description of the Related Art
Each wing of an airframe of an aircraft generally has a hollow structure and a wing panel forming a wing surface is fixed to a structural member in the wing by using fastener members (fasteners).
In so doing, the wing panel and structural member are fastened together by passing a pin-shaped fastener member, from outside the wing, through through-holes formed in both the wing panel and the structural member in the wing and fixing a front-end portion of the fastener member with a fastening member (collar) from inside the wing.
Besides, in the wings and a fuselage, structural members other than the wing panels as well as fixing members for equipment are fixed and fastened by the fastener members.
In so doing, the pin-shaped fastener member is inserted by passing through respective through-holes formed in two members to be fastened together, and the front-end portion of the fastener member is fixed by the fastening member (collar), thereby fastening the two members together.
Incidentally, the number of the members such as the wing panel to be fixed is not limited to two.
For aircraft, thorough measures need to be taken against lightning for the purpose of explosion proofing. When an aircraft is struck by lightning, resulting in large current flowing through the wing panels and structural members of the main wings and the like, part or in some cases, all of the current flows through portions fastened by the fastener members and fastening members. Discharges known as electrical arcs (or thermal sparks) occur (hereinafter referred to as arcs) in any fastened portion where a value of the current exceeds a limit value of an allowable passing current. This is a phenomenon in which due to the current passing through the fastened portion, sudden temperature rises occur on a fastening interface of members constituting the fastened portion and mainly including conductive members, locally melting the members and producing sparks in the surrounding atmosphere. In many cases, molten material known as hot particles scatter from the molten portion. Internal spaces of wings, which generally combine fuel tanks, need to be provided with explosion-proof measures. Therefore, it is necessary to prevent arc discharges by suppressing generation of arcs or sealing arcs at the time of a lightning strike as well as to prevent ignition by keeping scattering hot particles from coming in contact with inflammable fuel vapor. Here, parts likely to contain inflammable fuel vapor include the insides of fuel tanks in the wings and fuselage, the insides of surge tanks (tanks in which vent scoops or burst disks are installed) generally installed on the wing tip side of the fuel tanks, the insides of fuel-system equipments, and the like.
Thus, a configuration is proposed in which, as shown in FIG. 7, a cap 3 made of an insulating material is mounted, covering a front-end portion 1a of a fastener member 1 and a metal fastening piece 2 fastened to the fastener member 1, with filling a sealant 4 into the cap 3, thereby closing a gap between the cap 3 and the front-end portion 1a of the fastener member 1 and the metal fastening piece 2 (see, for example, Japanese Patent Laid-Open No. 2010-254287).
In a fastening worksite where the fastener member 1 is used, as shown in FIG. 7A, the sealant 4 is filled into an internal space of the cap 3 before the cap 3 is mounted on the front-end portion 1a of the fastener member 1 and the metal fastening piece 2. Then, as shown in FIG. 7B, the cap 3 filled with the sealant 4 is put on the front-end portion 1a of the fastener member 1 and the metal fastening piece 2. Thereupon excessive sealant 4 in the cap 3 spills out of the cap 3 through an opening in the cap 3. As shown in FIG. 7C, when an end face 3a of the cap 3 on the opening side is pressed against a surface of a member 5 such as a wing panel, the spilt sealant 4 exists in the form of an annular bulge on an outer peripheral side of the cap 3 while being interposed between the cap 3 and member 5, thereby arks are confined at an interface between the cap 3 and member 5.